There is a disparity between the recommended location of loudspeakers for an audio reproduction system and the locations of loudspeakers that are practically possible in a given environment. Restrictions on loudspeaker placement in a domestic environment typically occur due to room shape and furniture arrangement. In an automotive environment, loudspeaker placement is usually determined by availability of space rather than optimised listening. Consequently, it may be desirable to modify signals from a pre-recorded media in order to improve on the staging and imaging characteristics of a system that has been configured incorrectly.
There is an increasing number of audio formats employing a number of different channel configurations. Until recently, only one-channel and two-channel media were available to consumers. However, the introduction of distribution media such as DVD-Video, DVD-Audio, and Super-Audio CD has made multichannel audio commonplace in domestic and automotive systems. This has meant, in many cases that there is a mismatch between the number of loudspeakers in a listening environment and the number of channels in the media. For example, it frequently occurs that a listener has only two loudspeakers but 5 channels of audio on a medium. The converse case also exists where it is desirable to play two-channel program material distributed over more than two loudspeakers. Consequently algorithms are constantly being developed in order to adapt media from one format to another. Downmix algorithms reduce the number of audio channels and upmix algorithms increase the number.
Standard recommendations for domestic and automotive sound reproduction systems state that all loudspeakers should not only be placed correctly but have matched characteristics (i.e. ITU-R BS-775). However, in typical situations, this ideal requirement is rarely met. For example, in a domestic environment, it is often the case that the built-in audio system of a television is used for the centre channel of a surround sound system. This speaker rarely matches the larger, exterior loudspeakers used for the front left and right channels. In addition, it is typical for the surround speakers to be smaller as well. Consequently, the audio signals produced by these different loudspeakers differ too much for a cohesive sound field to be created in the listening environment. Therefore, it is desirable that these differences be minimised in order to give the impression of matched loudspeaker characteristics.
The tuning of high-end automotive audio systems is increasingly concentrating on the imaging characteristics and “sound staging.” It is a challenge to achieve staging similar to that intended by the recording engineer (as is possible in a domestic situation) due to the locations of the various loudspeakers in the car. It is therefore desirable that an automatic method of choosing delay and gain parameters for the various loudspeaker drivers in an automotive environment be developed to provide a “starting point” for tuning of the car's playback system.